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70-75 PSI are the magic numbers for these motors. 77 PSI is the highest I have ever measured on one. Be sure to check compression when the block is cold and dry and crank the motor over until maximum reading is reached. Usually 3-4 pulls on the recoil. Checking compression when the block is still warm from running may give a false low reading and adding oil or fuel to the cylinders will give a false higher compression reading. Good news is that they ran on a 16:1 gas to oil mixture so finding one with acceptable compression is not hard these days. Most of them were put out of service by worn out primer pump seals and or rotten cork floats long before the cylinders wore out and lost compression.